A new method of corrosion monitoring

Date added: 2022-06-26

Metal elements of ocean engineering structures are exposed to corrosion damage caused by contact with salt water. Corrosion can cover the entire surface of the tested structure, but it can also take the form of point damage, i.e. pits. Beata Zima, PhD, Eng. from the Institute of Ocean Engineering and Ship Technology is working on creating such a method of monitoring the progress of destruction that allows to assess global damage and to detect potential cracks and pitting.

The project "Monitoring the technical condition of metal structures subjected to corrosion degradation" received PLN 1,063,460 in funding in the SONATA competition organized by the National Science Center.

During the works on the project, Beata Zima, PhD will use the so-called non-destructive techniques, or, more precisely, the analysis of structural vibrations. - I will excite vibrations, then I will register signals at selected points in the structure, trying to create an algorithm to assess the global level of degradation based on the readings, as well as where the point damage is and what size it is.

Two methods of monitoring

As for monitoring, the scientist will use two methods: low-frequency and high-frequency. - The first one involves inducing vibrations with, for example, a hammer. The second method is to excite ultrasonic waves. Due to the advantages and disadvantages of both approaches, the planned methods will be based on both of them. However, it is not possible to detect, accurately locate and estimate the size of a very small point damage using the low-frequency method. Yet the low-frequency method can be useful in a global assessment of structural health. The high-frequency method, which is very effective in detecting cracks or pits, "comes in handy", says Beata Zima, PhD, Eng..

Model improvement, construction tests and special equipment

Work on the non-destructive assessment of the condition of corroded structures is nothing new. As PhD Zima notes, there are some simplifications, however. - There are many methods of wave propagation, but the usual assumption is that corrosion causes a uniform thickness variation. The corroded structure has a variable thickness, irregular surface, and there are also corrosion products with different parameters than the non-corroded part. Therefore, considering such a structure as homogeneous is a simplification. We want to check whether it is possible to obtain better results if we treat the structure as a sandwich structure and take into account the variable thickness. By improving the model, we should improve the credibility of new and existing algorithms, emphasizes Beata Zima.

Usually, the thickness of a corroded structure is tested at one point. To check the changes, e.g. in a 300-meter ship, it would be necessary to measure hundreds of such points, which is extremely time-consuming and costly. - The algorithms that we are planning to develop are to enable inference about the state of the entire structure after excitation and registration of vibrations in a much smaller number of points - she emphasizes.

After the end of the project, scientists want to develop a special device that would be used to diagnose objects exposed to corrosion degradation.

Three universities take part in the project: Gdańsk University of Technology, Goethe University in Frankfurt and the University of Lisbon.

Work on the project has already started and is expected to last three years.

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